A shallow trench isolation (STI) process for forming an element isolation region is easier than a local oxidation of silicon (LOCOS) process due to the miniaturization of semiconductor devices.
Conventionally, the STI (Shallow Trench Isolation) process proceeds as follows. First, a trench is formed by dry-etching a semiconductor substrate. The damage caused by dry-etching is curied. Then an oxide layer is formed inside of the trench by thermal oxidization in order to improve surface properties, and to achieve a rounding profile of an edge between an active area and an isolation area.
Next, an oxide layer is thickly deposited on the entire surface of the substrate to fill up the trench (a lining oxide is formed in the trench in advance of this filling). Then, the semiconductor substrate is planarized by chemical mechanical polishing.
Depending on the degree of integration of the semiconductor device being fabricated, an active area defined by the shallow trench isolation structure includes a narrow active area and a wide active area. The oxide is more thickly formed on the wide active area than on the narrow active area.
Therefore, a further process is performed between forming the oxide layers on the narrow active area and the wide active area. If a chemical mechanical polishing process is performed with focus on the wide active area, peeling damage occurs in the narrow active area. This damage deteriorates the performance and reliability of the fabricated semiconductor device.
To clarify multiple layers and regions, the thickness of the layers are enlarged in the drawings. Wherever possible, the same reference numbers will be used throughout the drawing(s) and accompanying written description to refer to the same or like parts. As used in this patent, stating that any part (e.g., a layer, film, area, or plate) is in any way positioned on (e.g., positioned on, located on, disposed on, or formed on, etc.) another part, means that the referenced part is either in contact with the other part, or that the referenced part is above the other part with one or more intermediate part(s) located therebetween. Stating that any part is in contact with another part means that there is no intermediate part between the two parts.